AUSTIN, Texas (CNN) -- Sen. Hillary Clinton, needing a win in Texas to derail Sen. Barack Obama in the race for the Democratic presidential nomination, sought Thursday to contrast her opponent's rhetorical skills with what she called her superior ability to govern.

Sens. Barack Obama and Hillary Clinton face off in a high-stakes debate.

"I do think that words are important and words matter," Clinton said at a debate at the University of Texas. "But actions speak louder than words."

Obama responded by laying out issues he's worked on in the Senate and others he'd support as president -- then called it ridiculous to suggest his supporters are "being duped."

"The implication is that the people who have been voting for me or involved in my campaign are somehow delusional," he said.

Obama said his supporters perceive the reality of what's going on in Washington very clearly, and they want to see it change.

"What they see is that if we don't bring the country together, stop the endless bickering, actually focus on solutions and reduce the special interests that have dominated Washington, then we will not get anything done." Watch Obama talk about his plan to change Washington »

The debate was the first the two have participated in since they met in Los Angeles January 31.

Five days later, the two effectively split the victories on Super Tuesday. But since then, Obama has rolled to 11 straight wins, a streak that leaves Clinton needing wins in delegate-rich Texas and Ohio on March 4.

Vermont and Rhode Island also hold primaries that day. Texas is the biggest prize, with 193 Democratic delegates.

Responding to a question from the panel, Clinton's sharpest attack on Obama came when she went after him for borrowing lines from a speech by Massachusetts Gov. Deval Patrick, his campaign co-chairman, in his own campaign speeches. The Clinton campaign has called that plagiarism.

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"If your campaign is going to be about words, they should be your own words," she said. "Lifting whole passages isn't change you can believe in; it's change you can Xerox." Watch the spat over plagiarism »

Some in the audience booed Clinton for the line.

"This is where we start getting into silly season in politics," Obama replied, saying Patrick is a friend who suggested he use the lines. "People start getting tired of it."

In the survey, taken before Obama's Tuesday victories in Wisconsin and Hawaii, 50 percent of likely Democratic primary voters support Clinton as their choice for the party's nominee, with 48 percent backing Obama. The poll's margin of error is 4.5 percentage points.

Two other recent polls also show the race statistically even.

With so much at stake, analysts said Clinton needed a very strong performance in the debate, the only time the two candidates will share a stage in Texas before the state's primary.

"Texas is the endgame. Hillary Clinton has to stop Obama in Texas. This means she has to do something to shake the race up. She has to raise doubts about Obama and get Democrats to rethink whether they really want to rally behind him," Schneider said.

In a state where Hispanic voters are expected to make up a large share of the March 4 electorate, the pair fielded questions on immigration reform and dealing with Cuba's government in the wake of President Fidel Castro's decision this week to step down. Watch the candidates talk about Cuba »

Both Clinton and Obama voted to authorize President Bush to build a border fence between the United States and Mexico -- but both said Thursday they would consult with leaders in border areas about where fencing is needed and where other methods could be used to secure the borders. Watch the candidates debate immigration »

"As with so much, the Bush administration has gone off the deep end," Clinton said.

Both also said they'd be willing to meet with Fidel Castro's brother Raul -- who is expected to become president of Cuba after his brother stepped down -- if the nation's leadership has shown signs of improving its record on human rights, freedom of the press and other issues.

Schneider said neither candidate appeared to have gained or lost significant ground in Thursday's debate. After months of campaigning that have included 19 Democratic debates, some analysts said the two may be satisfied to stand on the themes they've established and simply let voters decide.E-mail to a friend